1. Field of the Invention
The present invention relates to backlighting systems used with liquid crystal displays, and more particularly to light pipe systems.
2. Description of the Related Art
Liquid crystal displays (LCD's) are commonly used in portable computer systems, televisions and other electronic devices. An LCD requires a source of light for operation because the LCD is effectively a light valve, allowing transmission of light in one state and blocking transmission of light in a second state. Backlighting the LCD has become the most popular source of light in personal computer systems because of the improved contrast ratios and brightness possible. Because conventional monochrome LCD's are only approximately 12% transmissive and color LCD's are only approximately 2% transmissive, relatively large amounts of uniform light are necessary to provide a visible display. If power consumption and space were not of concern, the necessary level and uniformity of backlight could be easily obtained.
However, in portable devices power consumption (which directly effects battery life) and space are major concerns. Thus, there is a need to obtain a sufficiently uniform and bright backlight level with as little power as possible in as little space as possible at, of course, the lowest possible cost.
Numerous designs exist which trade off various of these goals to achieve a balanced display. Several of these designs, such as light curtains and light pipes, are shown in the drawing figures and will be described in detail. Such designs generally trade off uniformity of backlighting for space or power efficiency. These designs utilize various scattering means and a final diffuser before the light is presented to the LCD. The scattering means and the diffusers both contribute to loss of light and thus reduce the efficiency of the transfer of light from the light source to the LCD. While the designs are adequate in some cases, the demands for longer battery life with monochrome LCD's or adequate battery life with color LCD's are present, as is a desire for the use of less space.